You are maybe getting this the wrong way around. Folan was formed by Fredrik Olsson and LArs Nilsson (FOLAN). Husaberg turned to Lars Nilsson for their first engine design as Lars specailities were in making molds for casting and designing the rotating internals of the bottom end (gearbox, clutch etc). With that in mind, you could say that an early Husaberg looks very similar to a Folan!
Both Folan and Husaberg was using the same casting factory (forgot the name) and also machine shop (http://www.esw.nu). ESW was machining crank cases, covers, heads for Husaberg until it all was moved to Austria in 2004.